The proposal is to expand our original project organized to study how pigeons process duration discriminations. The proposed experiments will extend and clarify results from the original project and test new hypotheses regarding the functional components of the processing sequence involved in duration discriminations. The main focus will be on the interrelationships among timing, coding and stimulus selection. The first specific aim is to determine whether the tendency for pigeons to summate successive duration stimuli is related to whether or not those stimuli are associated with a common test stimulus. This specific aim examines the relationship between stimulus equivalence, coding, and timing. The second specific aim is to test the hypothesis that the same timing and coding processes are involved in choice and successive duration discriminations. The third specific aims is to measure the degree to which processing of event duration is influenced by signal characteristics and stimulus complexity. Proposed experiments will examine temporal summation, retention of duration events, the influence of variations in irrelevant characteristics of duration stimuli, and how effectively pigeons process duration signals when other relevant or irrelevant visual stimuli are concurrently available. The test procedures will involve training pigeons to respond to appropriate visual stimuli for food reward, contingent on the duration of a preceding signal. These experiments will provide valuable new information about memorial coding, timing, discrimination of temporal events, stimulus selection, and attention. This knowledge will contribute to an understanding of basic cognitive processes relevant to questions about brain function. The results will also have applied significance for mental health issues and human welfare, ranging from a better understanding of memory disorders to the development of better educational and therapeutic techniques pertinent to behavior and cognitive disorders.